Electro-Hydraulic Control System for Transmission with Dual-Area Piston for Torque-Transmitting Mechanism

ABSTRACT

An electro-hydraulic control system is provided for a transmission with a torque-transmitting mechanism that has a dual area piston. When pressurized fluid is provided to a first of the two piston areas, the position of a spring-biased shift valve controls whether pressurized fluid communicates with the second piston area. A solenoid valve in fluid communication with the shift valve is energizable to direct pressurized fluid to the shift valve to urge the shift valve to the unstroked position to which the spring also urges. The shift valve may also be urged by pressurized fluid to the stroked position, but only when the solenoid valve is not energized. The spring maintains the shift valve in the unstroked position when pressurized fluid is directed to the shift valve to act both against and with the spring.

TECHNICAL FIELD

The invention relates to an electro-hydraulic control system for atransmission; specifically, for pressurizing one or both areas of adual-area piston to engage a torque-transmitting mechanism.

BACKGROUND OF THE INVENTION

Dual-area apply pistons have two piston areas to which pressurized fluidmay be individually fed in order to engage a torque-transmittingmechanism. During operating conditions in which a high torque capacityis required, such as in a low range or a starting gear to handle stalltorque, both piston areas are fed pressurized fluid. Because pressurizedfluid is thus applied over a greater area, a larger force is applied toengage the torque-transmitting mechanism, resulting in a larger torquecapacity (also referred to as clutch capacity). During operatingconditions in which less torque capacity is required, such as whenoperating in higher speed ratios, only one of the piston areas is fedpressurized fluid, thus engaging the torque-transmitting mechanism, butat a lesser torque capacity and with a faster fill time of the clutchcavity. Typically, a dual-area piston requires the use of two separatetrim systems to direct pressurized fluid to each separate piston areafill cavity (i.e., each fill cavity typically requires a separate,dedicated solenoid valve and trim valve that direct pressurized fluid tothe fill cavity when the solenoid valve is energized).

SUMMARY OF THE INVENTION

A torque-transmitting mechanism engagable by application of a dual-areapiston allows the ability to operate the torque-transmitting mechanismat a lower torque capacity when appropriate, which may reduce theoverall pump size required for the hydraulic control system thatcontrols engagement of the torque-transmitting mechanism and allowfaster clutch cavity fill times. A high clutch gain (i.e., the ratio oftorque capacity (lb.-ft.) to main pressure of the control system (poundsper square inch) results in more shift-to-shift variation and moretemperature inconsistency. Thus, the ability to operate at a lowertorque capacity when appropriate improves shift quality, and results inbetter shift consistency.

An electro-hydraulic control system is provided that utilizes a singletrim system to direct pressurized fluid to one or both fill cavities ofa dual-area apply piston by providing a dedicated solenoid valve and aspring-biased shift valve responsive to energizing of the solenoidvalve. Specifically, an electro-hydraulic control system is provided fora multi-speed transmission having a plurality of torque-transmittingmechanisms including a selectively engagable torque-transmittingmechanism engagable by application of fluid pressure to a dual-areapiston with a first piston area and a second piston area, and a sourceof pressurized fluid. The electro-hydraulic control system includes ashift valve (SV3) movable between a stroked position (pressure-set) andan unstroked position (spring-set). A spring urges the shift valve tothe unstroked position. The shift valve permits pressurized fluid thatis in fluid communication with the first piston area to also be in fluidcommunication with the second piston area when the shift valve is in theunstroked position such that pressurized fluid is applied to both of thepiston areas to engage the torque-transmitting mechanism with thedual-area piston. The shift valve blocks the pressurized fluid from thesecond piston area when in the stroked position so that the pressurizedfluid is applied only to the first piston area to engage thetorque-transmitting mechanism with the dual-area piston. A solenoidvalve (SS1) is in fluid communication with the shift valve and isenergizable to thereby direct pressurized fluid to the shift valve toact on the shift valve with the spring to further urge the shift valveto the unstroked position. Pressurized fluid may also be applied to acton the shift valve against the spring, and provides an equal butopposite force on the shift valve to that of the pressurized fluid fromsolenoid valve (SS1), resulting in the spring force pushing the valve tothe unstroked position. When solenoid valve (SS1) is off and pressurizedfluid acts on the valve against the spring, the valve will stroke. Whensolenoid valve (SS1) is on, the shift valve will be unstroked regardlessof whether pressurized fluid acts against the spring.

Preferably, a control regulator valve is in fluid communication with themain pressure source and regulates fluid at a main pressure supplied bythe main pressure source to a control pressure. The fluid directed bythe solenoid valve (SS1) to urge the shift valve to the unstrokedposition is at the control pressure, the fluid urging the shift valve tothe stroked position is also at the control pressure, and the fluidapplied to the dual-area piston is at the main pressure.

Preferably, the pressurized fluid that is in fluid communication withthe first piston area is selectively provided via a trim valve thatcommunicates pressurized fluid to a first logic valve. The first logicvalve (SV2) multiplexes the trim valve by directing the pressurizedfluid to the first piston area when the first logic valve is in a firstposition, and to another of the torque-transmitting mechanisms when thefirst logic valve is in a second position. As used herein, a valve is“multiplexed” when it has more than one function, such as when it isable to at least partially control engagement of more than onetorque-transmitting mechanism.

Preferably, a second logic valve (SV1) is in fluid communication withthe solenoid valve (SS1) and moves when the solenoid valve is energizedfrom a spring-set position, to which it is biased, to a pressure-setposition. A pressure switch (S7) in fluid communication with the secondlogic valve is pressurized when the second logic valve is in thepressure-set position. The second logic valve allows pressurized fluidto the other torque-transmitting mechanism (to which the first logicvalve multiplexes the trim valve) when the trim valve is stroked toallow pressurized fluid to the first logic valve, when the second logicvalve is in the pressure-set position, and when the first logic valve isin the pressure-set position. Furthermore, the second logic valve isconfigured to be latched in the pressure-set position by pressurizedfluid selectively applied to the second logic valve so that the secondlogic valve remains in the pressure-set position even when the solenoidvalve is no longer energized to thereby prevent the pressurized fluidacting on the shift valve against the spring from exhausting.

Preferably, the above-mentioned valves, as well as additional valves inthe control system, are configured to establish one of the speed ratiosif the electronic controller becomes inoperable during a first set ofthe speed ratios and to establish another of the speed ratios if theelectronic controller becomes inoperable during a second set of thespeed ratios. Thus, there are different predetermined failure modes fordifferent speed ratios.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a multi-speed transmissionhaving torque-transmitting mechanisms engaged and disengaged via anelectro-hydraulic control system within the scope of the invention,including a torque-transmitting mechanism engagable via a dual-areapiston;

FIG. 2 is a chart showing an engagement schedule of thetorque-transmitting mechanisms of the transmission of FIG. 1;

FIGS. 3A and 3B are a schematic representation of a hydraulic controlportion of the electro-hydraulic control system of FIG. 1 having valvesto control engagement and disengagement of the torque-transmittingmechanisms of FIG. 1;

FIG. 4 is a schematic representation in fragmentary view of thehydraulic control portion shown in FIG. 3B;

FIG. 5 is a table indicating the state of many of the valves shown inFIGS. 3A and 3B for each speed ratio of the transmission of FIG. 1; and

FIG. 6 is a schematic representation in fragmentary view of thehydraulic control portion shown in FIG. 3A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers represent thesame or corresponding parts throughout the several views, there is shownin FIG. 1 a powertrain 10. The powertrain 10 includes a power source orengine 12, a torque converter 14 and a multi-speed transmission 16. Thetorque converter 14 is connected with the engine 12 and with atransmission input member 18 via a turbine 20. Selective engagement of atorque converter clutch TCC allows the engine 12 to be directlyconnected with the input shaft 18, bypassing the torque converter 14.The input member 18 is typically a shaft, and may be referred to as aninput shaft herein. The torque converter 14 includes the turbine 20, apump 24 and a stator 26. The converter stator 26 is grounded to a casing30 through a typical one-way clutch that is not shown. A damper 28 isoperatively connected to the engaged torque converter clutch TCC forabsorbing vibration.

The transmission 16 includes a first planetary gear set 40, a secondplanetary gear set 50, a third planetary gear set 60, and a fourthplanetary gear set 70. The first planetary gear set includes a sun gearmember 42, a ring gear member 44, and a carrier member 46 rotatablysupporting a plurality of pinion gears 47 that intermesh with both thering gear member 44 and the sun gear member 42. The second planetarygear set 50 includes a sun gear member 52, a ring gear member 54, and acarrier member 56 rotatably supporting a plurality of pinion gears 57that intermesh with both the ring gear member 54 and the sun gear member52. The third planetary gear set 60 includes a sun gear member 62, aring gear member 64, and a carrier member 66 rotatably supporting aplurality of pinion gears 67 that intermesh with both the ring gearmember 64 and the sun gear member 62. The fourth planetary gear set 70includes a sun gear member 72, a ring gear member 74, and a carriermember 76 rotatably supporting a plurality of pinion gears 77 thatintermesh with both the ring gear member 74 and the sun gear member 72.

The transmission 16 further includes a plurality of torque-transmittingmechanisms, including the torque converter clutch TCC, two rotatingclutches: C1 and C2; and four stationary clutches C3, C4, C5 and C6.Torque is transferred from the input member 18 to an output member 80along various powerflow paths through the transmission 16 depending onwhich of the plurality of selectively engagable torque-transmittingmechanisms are engaged. A retarder 81 is operatively connected to theoutput shaft 80 and is controllable to slow the output shaft 80 duringcertain vehicle operating conditions. The retarder 81 may be any of themany types known to those skilled in the art. A retarder flow valve 83controls the flow of fluid into a cavity within the retarder 81.Additional fluid within the cavity further slows the output shaft 80.

The input member 18 is continuously connected for common rotation withsun gear members 42 and 52. The output member 80 is continuouslyconnected for common rotation with carrier member 76. C1 is selectivelyengagable to connect the input member 18 for common rotation with sungear members 62 and 72. C2 is selectively engagable to connect the inputmember 18 for common rotation with carrier member 66 and ring gearmember 74. C3 is selectively engagable to ground ring gear member 54 tothe transmission casing 30. C4 is selectively engagable to ground ringgear member 64, carrier member 56 and ring gear member 44 to thetransmission casing 30. C5 is selectively engagable to ground ring gearmember 74 and carrier member 66 to the transmission casing 30. C6 isselectively engagable to ground carrier member 46 to the transmissioncasing 30.

The selective engagement and disengagement of the torque-transmittingmechanisms is controlled by an electro-hydraulic control system 82,which is shown in further detail in FIGS. 3A and 3B. Theelectro-hydraulic control system 82 includes an electronic controller84, which may be one or more control units and is referred to as ECU inFIG. 1, as well as a hydraulic control portion 86 referred to as HYD inFIG. 1. The electronic controller 84 is programmable to provideelectrical control signals to the hydraulic control portion 86 toestablish the fluid pressures that control engagement and disengagementof the torque-transmitting mechanisms TCC, C1, C2, C3, C4, C5 and C6.The hydraulic control portion 86 is operatively connected to each of thetorque-transmitting mechanisms TCC, C1, C2, C3, C4, C5 and C6 by a fluidconnection illustrated only schematically as dashed lines in FIG. 1 andin more detail as various passages, solenoids and valves shown in FIGS.3A and 3B. The hydraulic control portion 86 provides pressurized fluidto apply pistons that apply pressure to the torque-transmittingmechanisms to cause frictional engagement of friction and reactionplates of the torque-transmitting mechanisms to establish the desiredoperative connections.

Referring to FIG. 2, an engagement schedule indicates with an “X” eachof the torque-transmitting mechanisms C1, C2, C3, C4, C5 and C6 that areengaged to establish each of nine forward speed ratios FWD1, FWD2, FWD3,FWD4, FWD5, FWD6, FWD7, FWD8, and FWD9, as well as a Neutral mode and areverse speed ratio REV1.

Referring again to FIG. 1, single-area apply pistons P1, P2, P3 and P4are in fluid communication with the pressurized fluid supplied by thehydraulic control portion 86 to engage the torque-transmittingmechanisms C1, C2, C3, and C4 according to the engagement schedule ofFIG. 2. A single-area apply piston has only one effective surface areato which fluid pressure is applied to cause engagement of the adjacenttorque-transmitting mechanism. Assuming a constant apply pressure,torque-transmitting mechanisms engaged by a single-area piston have asingle clutch capacity (i.e., torque capacity). Dual-area apply pistonsP5 and P6 are used to engage torque-transmitting mechanisms C5 and C6,respectively. The dual-area apply piston P5 has two piston areas, afirst piston area PA1, and a second piston area PA2, each with a fillcavity to which pressurized fluid may be separately routed by thehydraulic control portion 86 so that the apply piston P5 is applied withless force when pressurized fluid is supplied to only one of the pistonareas PA1 or PA2, and with greater force when pressurized fluid issupplied to both of the piston areas PA1 and PA2. As is apparent in FIG.2, torque-transmitting mechanism C5 is engaged in the first forwardspeed ratio FWD 1 and the reverse speed ratio REV1. In those speedratios, more torque is required at the output member 80, and thusgreater clutch capacity is required by torque-transmitting mechanism C5.However, in the second forward speed ratio FWD2, the torque required issignificantly less. By supplying pressurized fluid to only the firstpiston area PA1, hydraulic energy requirements are minimized. Adual-area piston P6 is also supplied to engage torque-transmittingmechanism C6 with pressurized fluid supplied to both a first piston areaand a second piston area in the first forward speed ratio FWD 1, andapplied to only the first piston area in the ninth forward speed ratioFWD9, as far greater clutch capacity is required in the first forwardspeed ratio FWD 1 than in the ninth forward speed ratio FWD9. Varioustypes of dual-area pistons are known to those skilled in the art oftransmission design, and any dual-area piston may be used for pistons P5and P6.

Together, FIGS. 3A and 3B represent the complete hydraulic controlportion 86, with the fragmented portions in each Figure connecting atlike-numbered passages, from top to bottom, passages 104, 182, 149, 151,153, 157, 172, 174 and 159. The hydraulic control portion 86 includes amain regulator valve 90, a control regulator valve 92, two EBF (exhaustback flow) regulator valves 94 and 109, a converter flow valve 96, and alube regulator valve 98. The main regulator valve 90 is in fluidcommunication with a hydraulic pump 100 that draws fluid from areservoir 102 for delivery to a main passage 104. The pump 100 andreservoir 102 constitute a main pressure source of pressurized fluid ata pressure referred to herein as “main pressure” or “line pressure”. Thecontrol regulator valve 92 is in fluid communication with the mainregulator valve 90, and establishes a reduced control pressure withinpassage 149, which may then be communicated to other valves as describedbelow. The EBF regulator valve 94 is operable to vent fluid withinpassage 106 to exhaust should an over pressurized condition occur, andthe EBF regulator valve 109 is operable to vent fluid within passage 153should an overpressurized condition occur. Pump 100 is an engine-drivenpump that draws fluid from reservoir 102 that is ultimately used toengage the torque-transmitting mechanisms of FIG. 1, to pressurize thevalves of FIGS. 3A and 3B, to provide lubrication pressure to alubrication system 110 and cooling fluid to a transmission coolingsystem 112.

A relief valve 114 is provided for the main pressure passage 104. A mainregulator control passage accumulator 116 is provided to accumulatecontrol pressure fluid in passage 118 when fluid at such pressure isprovided to that passage. A converter relief valve 120 is provided forpressure at the converter flow valve 96 to the torque converter feed122. A filter regulator valve 124 controls pressure through a filter 126for the lubrication fluid provided to lubrication feed 128.

The hydraulic control portion 86 includes many pressure control solenoidvalves, such as variable pressure-type solenoid valves PCS1, PCS2, PCS3,PCS4, PCS5, PCS6, and TCC, and shift-type (i.e., on/off type) solenoidvalves SS1 and SS2. Each solenoid valve is in electric signalcommunication with the electronic controller 84 and is actuated uponreceipt of a control signal therefrom. The solenoid valves PCS1, PCS2and PCS5 are normally high or normally open-type solenoid valves, whilethe remaining solenoid valves PCS3, PCS4, PCS6, TCC, SS1 and SS2 arenormally low or normally closed-type solenoid valves. As is well known,an open solenoid valve will distribute output pressure in the absence ofan electrical signal to the solenoid. As used herein, a normallyhigh-type solenoid is energized by a control signal to be placed in andto remain in a closed position (to prevent fluid flow therethrough),while a normally low-type valve is energized to be placed in and toremain in an open position (to allow fluid flow therethrough). Thevariable pressure-type solenoid valves are chosen as normally high-typeor normally-low type so that, should a power failure occur and theelectronic controller 84 is unable to energize the valves, the variablepressure-type solenoid valves, along with the trim valves, logic valvesand shift valves will “fail” to positions that establish apredetermined, favorable one of the available speed ratios. For example,if a power failure occurs when the transmission 16 is operating inreverse REV 1 or neutral, the valves will be positioned to establish theneutral state. If a power failure occurs while the transmission 16 isoperating in any of the first through fifth forward speed ratios, thevalves will be positioned to establish the fifth forward speed ratioFWD5. If a power failure occurs during the sixth forward speed ratioFWD6, the valves will be positioned to establish the sixth forward speedratio. If a power failure occurs during any of the seventh through ninthforward speed ratios FWD7-FWD9, the valves will be positioned toestablish the seventh forward speed ratio FWD7.

The hydraulic control portion 86 also includes a plurality of trimvalves 130, 132, 134, 136, 138 and 140. Trim valve 130, solenoid valvePCS1 and accumulator valve 142 are a first trim system that, as will befurther explained below, is multiplexed to control engagement anddisengagement of both clutch C1 and clutch C3. Trim valve 132, solenoidvalve PCS2, and accumulator valve 144 are a second trim system that ismultiplexed to control engagement and disengagement of both clutch C2and C3. Trim valve 134, solenoid valve PCS3, and accumulator valve 146are a third trim system that is multiplexed to control engagement anddisengagement of both clutch C3 and C5. Trim valve 136, solenoid valvePCS4, and accumulator valve 148 are a fourth trim system that controlsengagement of the clutch C4. Trim valve 138, solenoid valve PCS6,accumulator valve 150, and shift valve SV4 are a fifth trim system thatcontrols engagement and disengagement of clutch C6, which is a clutchthat has a dual-area apply piston. The trim valve 138, solenoid valvePCS6, accumulator valve 150, and shift valve SV4 interact to determinewhether pressurized fluid is supplied only to fill cavity C6A, forapplications of clutch C6 requiring less torque capacity (e.g., in theninth forward speed ratio FWD9; see FIG. 5), or whether pressurizedfluid is supplied to both fill cavities C6A and C6B, for applications ofclutch C6 requiring greater torque capacity (e.g., in the first andthird forward speed ratios, FWD1 and FWD3; see FIG. 5). Trim valve 140,solenoid valve PCS TCC, converter flow valve 96 and converter reliefvalve 120 are a sixth trim system that controls engagement of torqueconverter clutch TCC.

Solenoid valve SS1 and shift valve SV3 are a trim system that, alongwith a control pressure signal from passage 156, logic valve SV1, trimvalve 134, solenoid valve PCS3 and accumulator valve 146, controlsengagement and disengagement of clutch C5 and whether engagement is byfluid pressure supplied at a fill cavity C5A for the first piston areaPA1, so that the clutch C5 is engaged with a lesser torque capacity, orby fluid pressure supplied to fill cavity C5A and to a fill cavity C5Bfor a the second piston area PA2 as well, so that the clutch C5 isengaged with a higher torque capacity. For each trim system, actuationof the associated solenoid valve causes actuation of the respective trimvalve and clutch (or one of the respective clutches in the case ofmultiplexed trim valves). Solenoid valve PCS5 and the main regulatorvalve 90 control the main pressure level in main passage 104 from thepump 100.

The hydraulic control portion 86 further includes logic valve SV2,referred to herein as a first logic valve, and logic valve SV1, referredto herein as a second logic valve. Solenoid SS1 receives an electricalcontrol signal from the electronic controller 84 to actuate or shift,thereby supplying fluid at control pressure from passage 159 to passage152 at the heads of valves SV1 and SV2, acting against bias springspositioned at the other end of the respective valves SV1 and SV2 thatbias the valves SV1 and SV2 upward against passage 152. As best viewedin FIG. 3B, when solenoid valve SS1 is energized, fluid at controlpressure in passage 152 is also supplied to the end of valve SV3 to actwith a bias spring 154 to force the head of the valve SV3 down againstpassage 156. Passage 156 is also filled with fluid at control pressurewhile SV1 is in the stroked position. As is clear from FIGS. 3A and 3B,the logic valves SV1 and SV2 are in fluid communication with the trimvalves 130, 132 and 134 and the respective solenoid valves PCS1, PCS2and PCS3; the energized or unenergized status of solenoid valves PCS1,PCS2 and PCS3 determines the positions of logic valves SV1 and SV2 andthus whether pressurized fluid is provided to fill cavities to engagetorque-transmitting mechanisms C1, C2, C3 and the fill cavity for thefirst piston area PA1 for C5, referred to as C5A. The logic valvesmultiplex the respective trim valves by allowing pressure directedthrough the trim valve to be directed to different clutches depending onthe position of the logic valve. For example, the logic valve SV2multiplexes trim valve 134 as it directs fluid pressure to fill cavityC5A, and then the first piston area PA1 of clutch C5 when in thespring-set position, but directs the pressurized fluid to a fluid cavityat clutch C3 when in the pressure-set (stroked) position. (The fluidcavities for the various torque-transmitting mechanism are representedas ports in FIGS. 3A and 3B, and are labeled “to C2”, to “C5A”, etc.)

When pressurized fluid is provided to fill cavity C5A, it may also beprovided to the fill cavity for the second piston area PA2 of clutch C5,referred to as C5B, if the shift valve SV3 is in a spring-set, unstrokedposition, as shown in FIG. 3B. The position of shift valve SV3 isdependent upon various factors. First, if solenoid valve SS1 isenergized, pressurized fluid is provided to passage 152 and acts withthe spring 154 to keep the shift valve SV3 in an unstroked position.This is true regardless of whether pressurized fluid (at the controlpressure) is in passage 156, as force of the control pressure fluid inpassage 152 acting on the shift valve SV3 with the force of the spring154 also acting on the shift valve SV3 will overcome the force ofcontrol pressure fluid in passage 152 acting on the shift valve SV3. Ifpressurized fluid is present in passage 156 but not in passage 152, theshift valve SV3 will be in the stroked position. Pressurized fluid willbe present in passage 156 at all times pump 100 is on, unless thepressurized fluid is exhausted through passage 153. The pressurizedfluid will exhaust through passage 153 when the logic valve SV1 is inthe spring-set or unstroked position. However, if logic valve SV1 is inthe pressure-set or stroked position, pressurized fluid in passage 156cannot exhaust, as the lowest land of logic valve SV1 blocks flow frompassage 156 to passage 153, as illustrated in FIG. 4. Logic valve SV1will be in the stroked position if solenoid valve SS1 is energized. Evenif solenoid valve SS1 is not energized, logic valve SV1 will be latchedin the stroked position if control pressure fluid is provided in passage157 while solenoid valve SS1 is still energized, prior to deenergizingsolenoid valve SS1. Because the control pressure fluid would then act ondifferent pressure responsive areas of the top two lands of logic valveSV1, with the lower of the two lands having a larger pressure responsivearea, logic valve SV1 will be “latched” (i.e., retained in a specificposition by fluid pressure) in a spring-set position and pressurizedfluid in passage 156 will not be able to exhaust. This latchingsituation occurs in speed ratios FWD2, FWD3, FWD4, ALT4, FWD5, and FWD6,as those skilled in the art will be able to readily determine based onthe information set forth in FIG. 5. Assuming control pressure fluid ispresent in passage 156, shift valve SV3 is in the spring-set positionwhen solenoid valve SS1 is energized, as control pressure fluid is thenapplied to both ends of valve SV3. However, as best viewed in FIG. 4,when shift valve SV3 is not energized, the fluid in passage 152 isexhausted and the control pressure fluid present in passage 156 inforward speed ratios will stroke the valve SV3, moving it to the strokedposition shown in FIG. 4, overcoming the bias of spring 154, andblocking the passage 158 so that pressurized fluid provided to fillcavity C5A cannot fill cavity C5B. Pressure switch PS7 is in fluidcommunication with the logic valve SV1 and is pressurized when logicvalve SV1 is in the pressure-set position.

Referring to FIG. 5, a table shows the steady-state conditions of thefollowing valves during available speed ratios (also referred to asranges): logic valves SV1 and SV2, switch valves SV3 and SV4, andpressure control solenoid valves PCS1, PCS2, PCS3, PCS4, PCS5, PCS6, PCSTCC and SS1. With respect to valves SS1, SV1, SV2, SV3, and SV4, an “0”in the chart indicates that the valve is in a spring-set position(“unstroked”) and a “1” indicates that the valve is in a pressure-setposition (“stroked”). Although not listed in the chart of FIG. 5, switchvalve SV5 is in a pressure-set position in any of the speed ratioswhenever vehicle operating conditions warrant application of theretarder 81 and, therefore, solenoid SS2 is energized. The speed ratioslisted in FIG. 5 correspond with those of the engagement chart of FIG.2, except optional alternate speed ratios ALT2, ALT 4 and ALT 8 arelisted and may be used in lieu of speed ratios FWD2, FWD4 and FWD8.

With respect to the columns in FIG. 5 for the respective pressurecontrol solenoid valves PCS1, PCS2, PCS3, PCS4, PCS6 and TCC, the clutchlisted for a particular speed ratio in a column for a particularsolenoid valve indicates that the state of the solenoid valve determineswhether pressurized fluid is communicated to that clutch during thatspeed ratio. If the box listing the clutch is not shaded, then thesolenoid is not energized in the case of a normally closed-type solenoidor is energized in the case of a normally open-type solenoid, and thelisted clutch is not engaged during that speed ratio. If the box isshaded, then the solenoid is energized in the case of a normallyclosed-type solenoid or is not energized in the case of a normally-opentype solenoid, and the listed clutch is thereby engaged during thatspeed ratio. The column of FIG. 5 labeled “Exhaust” indicates which ofthe clutches are being exhausted (emptied of pressurized fluid) duringeach of the various speed ratios.

The hydraulic control portion 86 is shown in the neutral state in FIGS.3A and 3B. Normally-high pressure control solenoids PCS1 and PCS2 areenergized to block flow of pressurized fluid therethrough. Pressurecontrol solenoid PCS3 is energized, so that trim valve 134 is in apressure-set position. The other trim valves 130, 132, 136, 138, 140, aswell as the logic valves SV1 and SV2 and switch valves SV3, SV4 and SV5are all shown in a spring-set position. It should be appreciated, thateach of these valves has two steady-state positions. That is, ifnormally-low pressure control solenoid PCS3 is not energized, the trimvalve 134 will slide upward from its position of FIG. 3B so that flow ofmain pressure fluid to passage 170 is blocked by the lowest land ofvalve 134. Similarly, if normally-high pressure control solenoid PCS1 isnot energized, trim valve 130 will move downward from its spring-setposition of FIG. 3A to a pressure set position in which flow of mainpressure fluid is permitted from passage 104 to passage 172. Ifnormally-high pressure control solenoid PCS2 is not energized, trimvalve 132 will move downward from its spring-set position of FIG. 3A toa pressure-set position in which flow of main pressure fluid ispermitted from passage 104 to passage 174. If normally-low pressurecontrol solenoid PCS4 is energized, trim valve 136 will move downwardfrom its spring-set position of FIG. 3A to a pressure-set position inwhich flow of main pressure fluid is permitted from passage 104 topassage 176. If normally-low pressure control solenoid PCS6 isenergized, trim valve 138 will move downward from its spring-setposition of FIG. 3A to a pressure-set position in which flow of mainpressure fluid is permitted from passage 104 to passages 178 and 180. Ifnormally-low pressure control solenoid PCS TCC is energized, trim valve140 will move downward from its spring-set position of FIG. 3A to apressure-set position in which flow of main pressure fluid is permittedfrom passage 104 to passage 182. If normally-high pressure controlsolenoid PCS5 is not energized, flow of control pressure fluid ispermitted from passage 149 to passages 160 and 118. If shift solenoidSS2 is energized, shift valve SV5 will move downward from its spring-setposition of FIG. 3A to a pressure set position in which flow of controlpressure fluid is permitted from passage 149 to passage 118, and to feedpassage 161. If shift solenoid SS1 is energized, control pressure fluidwill be provided to passage 152. The effect on movement of shift valvesSV1, SV2 and SV3 from the spring-set positions shown to pressure-setpositions is described with respect to the dual-area piston fillcavities C5A and C5B.

With respect to pressure control solenoid PCS5, in FIG. 3A, “MM/Rtdr”indicates that the pressure control solenoid PCS5 may be energized asnecessary to control an output pressure in passage 160 that controls apressure bias on the main regulator valve 90. When pressure controlsolenoid PCS5 is not energized, as shown in FIG. 3A, fluid at controlpressure established by the control pressure regulator valve 92 isprovided to passage 160. By varying the pressure within passage 118, thepressure control solenoid PCS5 is operable to vary the operatingcharacteristics of the main regulator valve 90, thereby modulating thepressure within the passage 104. The pressure control solenoid PCS5 andpassage 160 are in communication with passage 118 through a shift valveSV5 that shifts between a spring-set position (shown in FIG. 3A) and apressure-set position shown in FIG. 6, achieved when a solenoid valveSS2 is energized. The solenoid valve SS2 is energized during vehicledecelerations and other events when operation of the retarder 81 isdesirable. When shift valve SV5 is in the pressure-set position of FIG.6, control pressure is directed through feed passage 149 to feed passage161 which feeds the retarder flow valve 83 of FIG. 1 that controlsfilling of the retarder 81 and thus on/off operation of the retarder 81.When shift valve SV5 is in the pressure-set position, spring 155maintaining valve SV5 in the spring-set position is compressed, and thelands 163 and 165 move downward so that fluid from passage 149 is incommunication with feed passage 161 and with passage 118. Controlpressure is sent through valve SV5 to passage 118. Thus, controlpressure is applied to the top land 167 of the main regulator valve 90,and the main regulator valve 90 has “full line modulation”, which isdesirable during retarder operation. That is, with control pressureapplied at the top of land 167, additional pressure is placed on spool169 via spring 171, resulting in “full line modulation” of the mainregulator valve 90 and the main pressure. This prevents fluid at mainpressure in passage 104 from communicating with the torque converterfeed 122 and lubrication system 110, to better maintain full linepressure in passage 104, which is desirable during the same operatingconditions that retarder operation is desirable, as additional drivelineenergy is used by the pump 100 to provide the higher pressure. Whennormally-high pressure control solenoid valve PCS5 is energized andnormally-low solenoid valve SS2 is not energized as illustrated in FIG.3A, the fluid in passages 160 and 118 is at a lower trim pressure,rather than at control pressure, and this lower pressure is provided tothe top land 167. This results in “minimum line modulation” by the mainregulator valve 90, as line pressure in passage 104 is more readilyprovided to the torque converter feed 122 and the lube system 110. Theelectronic controller 84 can continuously adjust the pressure controlsolenoid valve PCS5 to modulate pressure in passage 118 based on enginetorque transmitting through the transmission 16, resulting in a closedloop control condition referred to herein as “variable line modulation”of the main regulator valve 90 and the main pressure. Information ofengine torque is provided via sensors and may be relayed from a separateengine control module to the electronic controller 84.

The position of shift valve SV5 also affects the position of a retarderregulator valve 162 that functions to adjust the pressure within theretarder 81 of FIG. 1. When the retarder regulator valve 162 is in thespring-set position shown in FIG. 3A (i.e., biased by spring 179), feedpassage 164 (which provides fluid to the retarder 81 to control pressurein the retarder cavity) exhausts through the exhaust port 175. Whenshift solenoid SS2 is energized and normally-high pressure controlsolenoid valve PCS5 is energized, valve SV5 is in the pressure-setposition shown in FIG. 6, fluid at trim pressure is directed throughpassage 166 to move the retarder regulator valve 162 to a pressure-setposition in which land 173 is moved downward against spring 179 and land177 blocks exhaust port 175, to prevent fluid at main pressure fed tothe retarder feed passage 164 from venting and thereby increasingpressure in the retarder 81.

As is apparent from the chart of FIG. 5, the pressure control solenoidPCS1 and the first trim system of which it is a part is multiplexed tocontrol the engagement and disengagement of both clutches C1 and C3. Thepressure control solenoid PCS2 and the second trim system of which it isa part is multiplexed to control the engagement and disengagement ofboth clutches C2 and C3. The pressure control solenoid PCS3 and thethird trim system of which it is a part is multiplexed to control theengagement and disengagement of both clutches C3 and C5. Pressurecontrol solenoid PCS4 controls the engagement of the clutch C4. Pressurecontrol solenoid PCS5 controls the pressure through passage 118 to themain regulator valve 90, as discussed above, to determine whether themain regulator valve 90 performs variable modulation of line pressure orfull modulation of line pressure. Pressure control solenoid PCS6controls the engagement of clutch C6. Pressure control solenoid PCS TCCcontrols the engagement of the torque converter clutch TCC shown inFIG. 1. The dashed lines in the chart of FIG. 5 indicate that therespective pressure control solenoid and trim system are decoupled fromthe respective clutch. The column labeled “Exhaust” indicates, for eachspeed ratio range, clutches that are being exhausted through the logicvalves. The remaining clutches that are not engaged are exhaustedthrough the associated trim valves. Referring to FIGS. 3A and 3B,passages labeled “EX” indicate exhaust passages that allow pressurizedfluid to exhaust, resulting in a non-pressurized state of passages andpressure switches in fluid communication with the exhaust passage.

Electrical signals are also sent to the electronic controller 84 basedon fluid pressure in the hydraulic control portion 86 to providefeedback information such as information indicative of valve positions.The locations of various pressure switches which provide such feedbackare indicated as pressure switches PS1, PS2, PS3, PS4, PS5, PS6, PS7 andPS8 in FIGS. 3A and 3B. Each pressure switch can monitor and report ahigh logic state and a low logic state, corresponding with a relativelyhigh pressure and low pressure, respectively, of the fluid at theswitch. The pressure switches are configured to report the high logicstate at or above a predetermined pressure and the low logic state belowthe predetermined pressure. Accordingly, as used herein, a “relativelyhigh pressure” is a pressure at or above a predetermined pressure and a“relatively low pressure” is a pressure below the predeterminedpressure. The ability to monitor the above-mentioned valves and detect achange, or lack of change, in valve position is of importance to providecontinuous and reliable operation of the transmission 16.

The pressure switches PS1, PS2, PS3, PS4, PS5, PS6, PS7, PS8, and theelectronic controller 84 that analyses the state of the pressureswitches form a diagnostic system for the transmission 16. Each pressureswitch PS1, PS2, PS3, PS4, PS5, PS6, PS7 and PS8 is operativelyconnected with the controller 84 by a transfer conductor (e.g., anelectrical wire) capable of carrying electrical signals therebetween.The controller 84 contains data representing the expected logic state ofeach of the pressure switches in each of the speed ratio ranges in whichthe transmission 16 operates. If one or more of the pressure switchesdetects and reports a logic state to the controller 84 that does notcorrespond to the expected logic state of that particular pressureswitch in the particular speed ratio in which the transmission 16 isoperating, the controller 84 will determine whether it is necessary toshift the transmission 16 to a different speed ratio range, including toone of the predetermined drive-home modes (also referred to as failuremodes), discussed below, until the transmission 16 can be maintenanced.

Those skilled in the art will understand the various fluid pressuresresulting in the passages shown in FIGS. 3A and 3B and the affect on thepositions of the trim valves, shift valves and logic valves, based onthe chart of FIG. 5. In the reverse speed ratio REV1, solenoids PCS1 andPCS3 are energized, and diagnostic pressure switches PS2, PS3 and PS5report a high logic state. In the Neutral state, solenoids PCS1, PCS2,and PCS3 are energized and pressure switches PS3 and PS5 report a highlogic state. In the first forward speed ratio FWD1, solenoids SS1, PCS1,PCS2, PCS3 and PCS6 are energized, and diagnostic pressure switches PS3,PS5, PS6 and PS7 report a high logic state. In the alternate secondforward speed ratio ALT2, solenoids SS1, PC S2, PCS3 and PCS TCC areenergized, and diagnostic pressure switches PS1, PS3, PS5 and PS7 reporta high logic state. In the second forward speed ratio FWD2, solenoidsPCS2, PCS3 and PCS TCC are energized, and diagnostic pressure switchesPS1, PS3, PS5 and PS7 report a high logic state. In the third forwardspeed ratio FWD3, solenoids PCS2, PCS6 and PCS TCC are energized, anddiagnostic pressure switches PS1, PS5, PS6 and PS7 report a high logicstate. In the fourth forward speed ratio FWD4, solenoids PCS2, PCS4 andPCS TCC are energized, and diagnostic pressure switches PS1, PS4, PS5and PS7 report a high logic state. In the alternate fourth forward speedratio ALT4, solenoids SS1, PCS2, PCS4 and PCS TCC are energized, anddiagnostic pressure switches PS1, PS4, PS5, PS7 and PS8 report a highlogic state. In the fifth forward speed ratio FWD5, solenoids SS1, PCS2,PCS3 and PCS TCC are energized, and diagnostic pressure switches PS1,PS3, PS5, PS7 and PS8 report a high logic state. In the sixth forwardspeed ratio FWD6, solenoids SS1, and PCS TCC are energized, anddiagnostic pressure switches PS1, PS2, PS5, PS7 and PS8 report a highlogic state. In the seventh forward speed ratio FWD7, solenoids SS1,PCS1, PCS3 and PCS TCC are energized, and diagnostic pressure switchesPS2, PS3, PS5, PS7 and PS8 report a high logic state. In the alternateeighth forward speed ratio ALT8, solenoids SS1, PCS1, PCS4 and PCS TCCare energized, and diagnostic pressure switches PS2, PS4, PS5, PS7 andPS8 report a high logic state. In the eighth forward speed ratio FWD8,solenoids PCS1, PCS4 and PCS TCC are energized, and diagnostic pressureswitches PS2, PS4, PS5 and PS8 report a high logic state. In the ninthforward speed ratio FWD9, solenoids PCS1, PCS6 and PCS TCC areenergized, and diagnostic pressure switches PS2, PS5, PS6 and PS8 reporta high logic state.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. An electro-hydraulic control system for a multi-speed transmissionhaving a plurality of torque-transmitting mechanisms including aselectively engagable torque-transmitting mechanism engagable byapplication of fluid pressure to a dual-area piston with a first pistonarea and a second piston area, and a source of pressurized fluid,comprising: a shift valve (SV3) movable between a stroked position andan unstroked position and including a spring urging the shift valve tothe unstroked position; wherein the shift valve permits pressurizedfluid in fluid communication with the first piston area to the secondpiston area when in the unstroked position such that pressurized fluidis applied to both of the piston areas to engage the torque-transmittingmechanism; and wherein the shift valve blocks pressurized fluid from thesecond piston area when in the stroked position such that thepressurized fluid is applied only to the first piston area to engage thetorque-transmitting mechanism; a solenoid valve (SS1) in fluidcommunication with the shift valve and energizable to thereby directpressurized fluid to the shift valve acting on the shift valve with thespring to further urge the shift valve to the unstroked position;wherein the shift valve is urged by pressurized fluid acting on theshift valve against the spring to the stroked position only when thesolenoid valve is not energized; and wherein the spring maintains theshift valve in the unstroked position when pressurized fluid is directedto the shift valve to act on the shift valve both against and with thespring.
 2. The electro-hydraulic control system of claim 1, wherein themulti-speed transmission is operable in multiple speed ratios, andfurther comprising: a trim valve (134); a first logic valve (SV2)selectively movable between a first position and a second position;wherein the trim valve is operable to selectively communicatepressurized fluid to the first logic valve; and wherein the first logicvalve multiplexes the trim valve by directing pressurized fluid to thefirst piston area of the dual-area torque-transmitting mechanism when inthe first position and to another of the torque-transmitting mechanisms(C3) when in the second position.
 3. The electro-hydraulic controlsystem of claim 1, further comprising: a second logic valve (SV1) influid communication with the solenoid valve (SS1) and movable when thesolenoid valve is energized from a spring-set position, to which it isbiased, to a pressure-set position; and wherein the second logic valveis configured to be latched in the pressure-set position by pressurizedfluid selectively applied to the second logic valve so that the secondlogic valve remains in the pressure set position even when the solenoidvalve is no longer energized to prevent the pressurized fluid acting onthe shift valve against the spring from exhausting.
 4. Theelectro-hydraulic control system of claim 3, further comprising: apressure switch (S7) in fluid communication with the second logic valveand pressurized when the second logic valve is in the pressure-setposition
 5. The electro-hydraulic control system of claim 3, wherein thesecond logic valve allows pressurized fluid to said another of thetorque-transmitting mechanisms when the trim valve selectivelycommunicates pressurized fluid to the first logic valve, the secondlogic valve is in the pressure-set position, and the first logic valveis in the pressure-set position.
 6. The electro-hydraulic control systemof claim 1, further comprising: an electronic controller; additionalsolenoid valves operatively connected with the electronic controller andeach energizable upon receipt of a respective control signal from theelectronic controller; trim valves each selectively movable from a firstposition to a second position; wherein each of the additional solenoidvalves moves a different respective one of the trim valves whenenergized; additional logic valves movable in response to movement ofthe additional trim valves and wherein at least some of the additionallogic valves multiplex the additional trim valves by directingpressurized fluid to different ones of the torque-transmittingmechanisms; and wherein the additional trim valves and the additionallogic valves are configured to establish one of the speed ratios if theelectronic controller becomes inoperable during a first set of the speedratios and are configured to establish another of the speed ratios ifthe electronic controller becomes inoperable during a second set of thespeed ratios.
 7. The electro-hydraulic control system of claim 1,further comprising: a control regulator valve in fluid communicationwith the main pressure source and regulating fluid at a main pressuresupplied by the main pressure source to a control pressure; whereinfluid directed by the solenoid valve (SS1) to urge the shift valve tothe unstroked position is at the control pressure; wherein fluid urgingthe shift valve to the stroked position is at the control pressure; andwherein fluid applied to the dual-area piston is at the main pressure.8. An electro-hydraulic control system in combination with atransmission, comprising: six torque-transmitting mechanisms selectivelyengagable in different combinations to provide different speed ratios ofthe transmission; wherein the torque-transmitting mechanisms include aselectively engagable torque-transmitting mechanism engagable by adual-area piston having a first piston area and a second piston area;multiple solenoid valves; multiple trim valves, each movable in responseto energizing of a respective one of the solenoid valves; multiple logicvalves, each movable between a first and a second position in responseto movement of the trim valves; wherein each logic valve multiplexes arespective different one of the trim valves by directing pressurizedfluid to a different respective one of the torque-transmittingmechanisms when in the first position than when in the second position;a main pressure source providing fluid at a main pressure; a controlregulator valve in fluid communication with the main pressure source toregulate the main pressure to a control pressure; a shift valve (SV3)movable between a stroked position and an unstroked position; a springurging the shift valve to the unstroked position; wherein the shiftvalve permits fluid at the main pressure and in fluid communication withthe first piston area to the second piston area when in the unstrokedposition such that fluid pressure is applied to both of the piston areasto engage the torque-transmitting mechanism; wherein the shift valveblocks fluid at main pressure from the second piston area when in thestroked position such that fluid pressure is applied to only the firstpiston area to engage the torque-transmitting mechanism; an additionalsolenoid valve (SS1) in fluid communication with the shift valve andenergizable to thereby direct fluid at the control pressure to the shiftvalve to further urge the shift valve to the unstroked position; and alogic valve (SV1) in fluid communication with the shift valve andselectively movable between a pressure-set position and a spring-setposition.
 9. The electro-hydraulic control system of claim 8, whereinthe torque-transmitting mechanism with a dual-area piston ischaracterized by a first torque capacity when engaged by application offluid to the first piston area and by a second torque capacity whenengaged by application of fluid to the first and the second pistonareas.
 10. The electro-hydraulic control system in combination with atransmission of claim 8, further comprising: seven diagnostic pressureswitches each in fluid communication with a different respective one ofthe trim valves or the logic valves and each having a high and a lowlogic state corresponding with the respective first and second positionsof the trim valve or logic valve with which it is in fluidcommunication.
 11. An electro-hydraulic control system for a multi-speedtransmission having a plurality of torque-transmitting mechanismsincluding a selectively engagable torque-transmitting mechanismengagable by application of fluid pressure to a dual-area piston with afirst piston area and a second piston area, and a source of pressurizedfluid, comprising: a pressure control solenoid valve (PCS3); a trimvalve (134) movable from a first position to a second position when thepressure control solenoid valve is energized; a shift-type solenoidvalve (SS1); a shift valve (SV3) in fluid communication with theshift-type solenoid valve and with the second-piston area andselectively movable between a stroked position and an unstrokedposition; wherein the shift valve is in the unstroked position when theshift-type solenoid is energized; a first logic valve (SV2) in fluidcommunication with the trim valve, with the shift-type solenoid valve,with the shift valve, and with the first piston area; wherein the trimvalve directs pressurized fluid to the first logic valve when the trimvalve is in the second position; wherein the first logic valve isoperable to direct the pressurized fluid to the first piston area whenthe trim valve is directing the pressurized fluid to the first logicvalve; and wherein the shift valve blocks pressurized fluid directed tothe first logic valve from reaching the second piston area when theshift valve is in a stroked position and allows pressurized fluiddirected to the first logic valve to the second piston area when theshift valve is in an unstroked position.